Method and apparatus for transmitting signal in a wireless communication system

ABSTRACT

A method for transmitting a signal by a Device-to-Device (D2D) User Equipment (UE) in a wireless communication system is disclosed. The method includes determining a resource pool for a D2D control signal, determining a resource pool for a D2D communication signal based on the resource pool for a D2D control signal, and transmitting a D2D communication signal using the resource pool for a D2D communication signal. Subframes of the resource pool for a D2D communication signal were reindexed, starting from a first subframe following a last subframe of the resource pool for a D2D control signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(e), this application claims the benefit ofU.S. Provisional Patent Application No(s). 62/039,437, filed on Aug. 20,2014, 62/060,565, filed on Oct. 6, 2014 and 62/085,640, filed on Nov.30, 2014, the contents of which are all hereby incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system andmore particularly, to a method and apparatus for transmitting andreceiving a signal using frequency hopping in Device-to-Device (D2D)communication.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.) among them. Forexample, multiple access systems include a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system, and a Multi-Carrier FrequencyDivision Multiple Access (MC-FDMA) system.

D2D communication is a communication scheme in which a direct link isestablished between User Equipments (UEs) and the UEs exchange voice anddata directly with each other without intervention of an evolved Node B(eNB). D2D communication may cover UE-to-UE communication andpeer-to-peer communication. In addition, D2D communication may find itsapplications in Machine-to-Machine (M2M) communication and Machine TypeCommunication (MTC).

D2D communication is under consideration as a solution to the overheadof an eNB caused by rapidly increasing data traffic. For example, sincedevices exchange data directly with each other without intervention ofan eNB by D2D communication, compared to legacy wireless communication,the overhead of a network may be reduced. Further, it is expected thatthe introduction of D2D communication will simplify procedures of anevolved Node B (eNB), reduce the power consumption of devicesparticipating in D2D communication, increase data transmission rates,increase the accommodation capability of a network, distribute load, andextend cell coverage.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies onDevice-to-Device (D2D) hopping methods that can prevent resourcecollision.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The object of the present invention can be achieved by providing amethod for transmitting a signal by a Device-to-Device (D2D) UserEquipment (UE) in a wireless communication system, including determininga resource pool for a D2D control signal, determining a resource poolfor a D2D communication signal based on the resource pool for a D2Dcontrol signal, and transmitting a D2D communication signal using theresource pool for a D2D communication signal. Subframes of the resourcepool for a D2D communication signal were reindexed, starting from afirst subframe following a last subframe of the resource pool for a D2Dcontrol signal.

In another aspect of the present invention, provided herein is a UE fortransmitting a Device-to-Device (D2D) signal in a wireless communicationsystem, including a transmission module, and a processor. The processoris configured to determine a resource pool for a D2D control signal,determine a resource pool for a D2D communication signal based on theresource pool for a D2D control signal, and transmit a D2D communicationsignal using the resource pool for a D2D communication signal. Subframesof the resource pool for a D2D communication signal were reindexed,starting from a first subframe following a last subframe of the resourcepool for a D2D control signal.

The above aspects of the present invention may include all or a part ofthe followings.

The subframes may be reindexed with a modulo 10 operation, whileincreasing a subframe index, starting from a first subframe of theresource pool for a D2D communication signal.

If frequency hopping is used for transmission of the D2D communicationsignal, a lowest Physical Resource Block (PRB) indexes of PRBs to whichthe D2D communication signal is mapped may be changed between a firstPRB index and a second PRB index, according to a change of reindexedsubframe number.

If subband-based hopping is used for transmission of the D2Dcommunication signal, a slot index used in determining a PRB index maybe produced by performing reindexing, starting from a slot of a firstsubframe following a last subframe of the resource pool for a D2Dcontrol signal.

An initial value of a pseudorandom sequence generation function used indetermining the PRB index may be fixed to 0.

The number of subbands may be 2 or larger.

If a duplex mode of the D2D UE is Time Division Duplex (TDD), the firstsubframe may be an uplink subframe following a last subframe of theresource pool for a D2D control signal.

Advantageous Effects

According to the present invention, when hopping is used between D2D UEshaving different transmission patterns, resource collision can beprevented.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a radio frame structure;

FIG. 2 illustrates a structure of a downlink resource grid for theduration of one downlink slot;

FIG. 3 illustrates a structure of a downlink subframe;

FIG. 4 illustrates a structure of an uplink subframe;

FIGS. 5 and 6 illustrate frequency hopping;

FIGS. 7, 8, 9 and 10 illustrate a hopping method according to anembodiment of the present invention; and

FIG. 11 is a block diagram of a transmission apparatus and a receptionapparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments described below are constructed by combining elementsand features of the present invention in a predetermined form. Theelements or features may be considered optional unless explicitlymentioned otherwise. Each of the elements or features can be implementedwithout being combined with other elements. In addition, some elementsand/or features may be combined to configure an embodiment of thepresent invention. The sequential order of the operations discussed inthe embodiments of the present invention may be changed. Some elementsor features of one embodiment may also be included in anotherembodiment, or may be replaced by corresponding elements or features ofanother embodiment.

Embodiments of the present invention will be described focusing on adata communication relationship between a base station and a terminal.The base station serves as a terminal node of a network over which thebase station directly communicates with the terminal. Specificoperations illustrated as being conducted by the base station in thisspecification may be conducted by an upper node of the base station, asnecessary.

That is, it is obvious that various operations performed to implementcommunication with the terminal over a network composed of multiplenetwork nodes including a base station can be conducted by the basestation or network nodes other than the base station. The term “BaseStation (BS)” may be replaced with terms such as “fixed station”,“Node-B”, “eNode-B (eNB)”, and “access point.” The term “relay” may bereplaced with such terms as “Relay Node (RN)” and “Relay Station (RS)”.The term “terminal” may also be replaced with such terms as “UserEquipment (UE)”, “Mobile Station (MS)”, “Mobile Subscriber Station(MSS)”, and “Subscriber Station (SS)”.

It should be noted that specific terms used in the description below areintended to provide better understanding of the present invention, andthese specific terms may be changed to other forms within the technicalspirit of the present invention.

In some cases, well-known structures and devices may be omitted or blockdiagrams illustrating only key functions of the structures and devicesmay be provided, so as not to obscure the concept of the presentinvention. The same reference numbers will be used throughout thisspecification to refer to the same or like parts.

Exemplary embodiments of the present invention can be supported bystandard documents for at least one of wireless access systems includingan institute of electrical and electronics engineers (IEEE) 802 system,a 3rd Generation Partnership Project (3GPP) system, a 3GPP Long TermEvolution (LTE) system, an LTE-Advanced (LTE-A) system, and a 3GPP2system. That is, steps or parts which are not described in theembodiments of the present invention so as not to obscure the technicalspirit of the present invention may be supported by the above documents.All terms used herein may be supported by the aforementioned standarddocuments.

The embodiments of the present invention described below can be appliedto a variety of wireless access technologies such as Code DivisionMultiple Access (CDMA), Frequency Division Multiple Access (FDMA), TimeDivision Multiple Access (TDMA), Orthogonal Frequency Division MultipleAccess (OFDMA), and Single Carrier Frequency Division Multiple Access(SC-FDMA). CDMA may be embodied through radio technologies such asUniversal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may beembodied through radio technologies such as Global System for Mobilecommunication (GSM)/General Packet Radio Service (GPRS)/Enhanced Datarates for GSM Evolution (EDGE). OFDMA may be embodied through radiotechnologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802-20, and evolved UTRA (E-UTRA). UTRA is a part of the UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is a part of evolved UMTS(E-UMTS), which uses E-UTRA. 3GPP LTE employs OFDMA for downlink andemploys SC-FDMA for uplink. LTE-Advanced (LTE-A) is an evolved versionof 3GPP LTE. WiMAX can be explained by IEEE 802.16e standard(WirelessMAN-OFDMA reference system) and advanced IEEE 802.16m standard(WirelessMAN-OFDMA Advanced system). For clarity, the followingdescription focuses on 3GPP LTE and 3GPP LTE-A systems. However, thespirit of the present invention is not limited thereto.

LTE/LTE-A Subframe Structure/Channel

Hereinafter, a radio frame structure will be described with reference toFIG. 1.

In a cellular OFDM wireless packet communication system, an uplink(UL)/downlink (DL) data packet is transmitted on a subframe-by-subframebasis, and one subframe is defined as a predetermined time intervalincluding a plurality of OFDM symbols. 3GPP LTE supports radio framestructure type 1 applicable to Frequency Division Duplex (FDD) and radioframe structure type 2 applicable to Time Division Duplex (TDD).

FIG. 1(a) illustrates radio frame structure type 1. A downlink radioframe is divided into 10 subframes. Each subframe includes two slots inthe time domain. The duration of transmission of one subframe is definedas a Transmission Time Interval (TTI). For example, a subframe may havea duration of 1 ms and one slot may have a duration of 0.5 ms. A slotmay include a plurality of OFDM symbols in the time domain and aplurality of Resource Blocks (RBs) in the frequency domain. Since 3GPPLTE employs OFDMA for downlink, an OFDM symbol represents one symbolperiod. An OFDM symbol may be referred to as an SC-FDMA symbol or symbolperiod. A Resource Block (RB), which is a resource allocation unit, mayinclude a plurality of consecutive subcarriers in a slot.

The number of OFDM symbols included in one slot depends on theconfiguration of a Cyclic Prefix (CP). CPs are divided into an extendedCP and a normal CP. For a normal CP configuring each OFDM symbol, eachslot may include 7 OFDM symbols. For an extended CP configuring eachOFDM symbol, the duration of each OFDM symbol is extended and thus thenumber of OFDM symbols included in a slot is smaller than in the case ofthe normal CP. For the extended CP, each slot may include, for example,6 OFDM symbols. When a channel state is unstable as in the case of highspeed movement of a UE, the extended CP may be used to reduceinter-symbol interference.

When the normal CP is used, each slot includes 7 OFDM symbols, and thuseach subframe includes 14 OFDM symbols. In this case, the first two orthree OFDM symbols of each subframe may be allocated to a PhysicalDownlink Control Channel (PDCCH) and the other OFDM symbols may beallocated to a Physical Downlink Shared Channel (PDSCH).

FIG. 1(b) illustrates radio frame structure type 2. A type-2 radio frameincludes two half frames, each of which has 5 subframes, Downlink pilotTime Slots (DwPTSs), Guard Periods (GPs), and Uplink pilot Time Slots(UpPTSs). Each subframe consists of two slots. The DwPTS is used forinitial cell search, synchronization, or channel estimation in a UE,whereas the UpPTS is used for channel estimation in an eNB and ULtransmission synchronization of a UE. The GP is provided to eliminate ULinterference caused by multipath delay of a DL signal between DL and UL.Regardless of the types of radio frames, a subframe consists of twoslots.

The illustrated radio frame structures are merely examples, and variousmodifications may be made to the number of subframes included in a radioframe, the number of slots included in a subframe, or the number ofsymbols included in a slot.

FIG. 2 is a diagram illustrating a resource grid of one DL slot. One DLslot includes 7 OFDM symbols in the time domain and an RB includes 12subcarriers in the frequency domain. However, embodiments of the presentinvention are not limited thereto. For the normal CP, a slot may include7 OFDM symbols. For the extended CP, a slot may include 6 OFDM symbols.Each element in the resource grid is referred to as a Resource Element(RE). An RB includes 12 7 REs. The number NDL of RBs included in a DLslot depends on a DL transmission bandwidth. A UL slot may have the samestructure as the DL slot.

FIG. 3 illustrates a DL subframe structure. Up to three OFDM symbols inthe leading part of the first slot in a DL subframe corresponds to acontrol region to which a control channel is allocated. The other OFDMsymbols of the DL subframe correspond to a data region to which a PDSCHis allocated. DL control channels used in 3GPP LTE include, for example,a Physical Control Format Indicator Channel (PCFICH), a PhysicalDownlink Control Channel (PDCCH), and a Physical Hybrid Automatic RepeatreQuest (HARQ) Indicator Channel (PHICH). The PCFICH is transmitted inthe first OFDM symbol of a subframe, carrying information about thenumber of OFDM symbols used for transmission of control channels in thesubframe. The PHICH carries a HARQ ACK/NACK signal in response to uplinktransmission. Control information carried on the PDCCH is calledDownlink Control Information (DCI). The DCI includes UL or DL schedulinginformation or a UL transmit power control command for a UE group. ThePDCCH may deliver information about the resource allocation andtransport format of a DL Shared Channel (DL-SCH), resource allocationinformation of a UL Shared Channel (UL-SCH), paging information of aPaging Channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher-layer control message such as arandom access response transmitted on the PDSCH, a set of transmit powercontrol commands for individual UEs in a UE group, transmit powercontrol information, and Voice over Internet Protocol (VoIP) activationinformation. A plurality of PDCCHs may be transmitted in the controlregion. A UE may monitor a plurality of PDCCHs. A PDCCH is transmittedin an aggregation of one or more consecutive control channel elements(CCEs). A CCE is a logical allocation unit used to provide a PDCCH at acoding rate based on the state of a radio channel. A CCE corresponds toa plurality of RE groups. The format of a PDCCH and the number ofavailable bits for the PDCCH are determined depending on the correlationbetween the number of CCEs and the coding rate provided by the CCEs. AneNB determines the PDCCH format according to DCI transmitted to a UE andadds a Cyclic Redundancy Check (CRC) to the control information. The CRCis masked with an Identifier (ID) known as a Radio Network TemporaryIdentifier (RNTI) according to the owner or usage of the PDCCH. If thePDCCH is directed to a specific UE, its CRC may be masked with aCell-RNTI (C-RNTI) of the UE. If the PDCCH is for a paging message, theCRC of the PDCCH may be masked with a Paging Radio Network TemporaryIdentifier (P-RNTI). If the PDCCH delivers system information (morespecifically, a System Information Block (SIB)), the CRC may be maskedwith a system information ID and a System Information RNTI (SI-RNTI). Toindicate a random access response which is a response to a random accesspreamble transmitted by a UE, the CRC may be masked with a RandomAccess-RNTI (RA-RNTI).

FIG. 4 illustrates a UL subframe structure. A UL subframe may be dividedinto a control region and a data region in the frequency domain. APhysical Uplink Control Channel (PUCCH) carrying uplink controlinformation is allocated to the control region. A Physical Uplink SharedChannel (PUSCH) carrying user data is allocated to the data region. Tomaintain single carrier property, a UE does not simultaneously transmita PUSCH and a PUCCH. A PUCCH for a UE is allocated to an RB pair in asubframe. The RBs from an RB pair occupy different subcarriers in twoslots. This is called frequency hopping of the RB pair allocated to thePUCCH over a slot boundary.

PUSCH Hopping

To achieve frequency diversity, frequency hopping may be applied toPUSCH transmission. There are two types of frequency hopping in theLTE/LTE-A system: type 1 frequency hopping and type 2 frequency hopping.In the type 1 frequency hopping scheme, one of ¼, −¼, and ½ of a hoppingbandwidth is selected according to hopping bits indicated by UL grantDCI. Specifically, the lowest PRB index of a first slot is determined byn_(PRB) ^(S1)(i)=ñ_(PRB) ^(S1)(i)+Ñ_(RB) ^(HO)/2. n_(PRB)^(S1)(i)=RB_(START) where RB_(START) may be obtained from a UL grant.Once the lowest PRB index of the first slot is determined, the lowestPRB index of a second slot is determined by [Equation 1] and [Table 1].n _(PRB) ^(S1)(i)=ñ _(PRB) ^(S1)(i)+Ñ _(RB) ^(HO)/2n _(PRB)(i)=ñ _(PRB)(i)+Ñ _(RB) ^(HO)/2  [Equation 1]where N_(RB) ^(HO) is a hopping offset (pusch-HoppingOffset) rangingfrom 0 to 98. If N_(RB) ^(HO) is an odd number, Ñ_(RB) ^(HO)=N_(RB)^(HO)+1 and if N_(RB) ^(HO) is an even number, Ñ_(RB) ^(HO)=N_(RB)^(HO).

TABLE 1 System Number of Information BW Hopping in hopping N_(RB) ^(UL)bits bits ñ_(PRB) (i) 6-49 1 0 (└N_(RB) ^(PUSCH)/2┘ + ñ_(PRB) ^(S1) (i))mod N_(RB) ^(PUSCH) 1 Type 2 PUSCH Hopping 50-110 2 00 (└N_(RB)^(PUSCH)/4┘ + ñ_(PRB) ^(S1) (i)) mod N_(RB) ^(PUSCH) 01 (−└N_(RB)^(PUSCH)/4┘ + ñ_(PRB) ^(S1) (i)) mod N_(RB) ^(PUSCH) 10 (└N_(RB)^(PUSCH)/2┘ + ñ_(PRB) ^(S1) (i)) mod N_(RB) ^(PUSCH) 11 Type 2 PUSCHHopping

In [Table 1], N_(RB) ^(PUSCH) is the number of PUSCH RBs (i.e., ahopping bandwidth).

FIG. 5 illustrates an example of type 1 hopping. In FIG. 5, it isassumed that two hopping bits are set to 01. Thus, (−└N_(RB)^(PUSCH)/4┘+ñ_(PRB) ^(S1)(i)) mod N_(RB) ^(PUSCH). The lowest PRB indexn_(PRB)(i) of the second slot may be determined by [Equation 1], whichis hopped from the lowest PRB index of the first slot by −¼ of thehopping bandwidth.

If the hopping mode is inter-subframe in type 1 frequency hopping,first-slot resource allocation is applied to an even-numberedCURRENT_TX_NB and second-slot resource allocation is applied to anodd-numbered CURRENT_TX_NB. CURRENT_TX_NB represents the transmissionnumber for a transport block (TB) transmitted in slot n_(s).

Type 2 PUCCH hopping is based on subbands. If mirroring is not applied,the lowest PRB index of slot n_(s) is determined by [Equation 2].

$\begin{matrix}{{n_{PRB}\left( n_{s} \right)} = \left\{ \begin{matrix}{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)} & {N_{sb} = 1} \\{{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)} + \left\lceil {N_{RB}^{HO}/2} \right\rceil} & {N_{sb} > 1}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$where N_(sb) is the number of subbands indicated by higher-layersignaling. ñ_(PRB)(n_(s)) is given as [Equation 3].

$\begin{matrix}{{{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)} = {\left( {{\overset{\sim}{n}}_{VRB} + {{f_{hop}(i)} \cdot N_{RB}^{sb}} + {\left( {\left( {N_{RB}^{sb} - 1} \right) - {2\left( {{\overset{\sim}{n}}_{VRB}{mod}\; N_{RB}^{sb}} \right)}} \right) \cdot {f_{m}(i)}}} \right){{mod}\left( {N_{RB}^{sb} \cdot N_{sb}} \right)}}}\mspace{20mu}{i = \left\{ {{\begin{matrix}\left\lfloor {n_{s}/2} \right\rfloor & {{inter}\text{-}{subframe}\mspace{14mu}{hopping}} \\n_{s} & {{intra}\mspace{14mu}{and}\mspace{14mu}{inter}\text{-}{subframe}\mspace{14mu}{hopping}}\end{matrix}\mspace{20mu}{n_{PRB}\left( n_{s} \right)}} = \left\{ {{\begin{matrix}{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)} & {N_{sb} = 1} \\{{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)} + \left\lceil {N_{RB}^{HO}/2} \right\rceil} & {N_{sb} > 1}\end{matrix}\mspace{20mu}{\overset{\sim}{n}}_{VRB}} = \left\{ \begin{matrix}n_{VRB} & {N_{sb} = 1} \\{n_{VRB} - \left\lceil {N_{RB}^{HO}/2} \right\rceil} & {N_{sb} > 1}\end{matrix} \right.} \right.} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

A hopping function ƒ_(hop)(i) is given as [Equation 4].

                                     [Equation  4]${f_{hop}(i)} = \left\{ \begin{matrix}0 & {N_{sb} = 1} \\{\left( {{f_{hop}\left( {i - 1} \right)} + {\sum\limits_{k = {{i \cdot 10} + 1}}^{{i \cdot 10} + 9}\;{{c(k)} \times 2^{k - {({{i \cdot 10} + 1})}}}}} \right){mod}\; N_{sb}} & {N_{sb} = 2} \\{\begin{pmatrix}{{f_{hop}\left( {i - 1} \right)} + \left( {\sum\limits_{k = {{i \cdot 10} + 1}}^{{i \cdot 10} + 9}\;{{c(k)} \times 2^{k - {({{i \cdot 10} + 1})}}}} \right)} \\{{{mod}\;\left( {N_{sb} - 1} \right)} + 1}\end{pmatrix}{{mod}N}_{sb}} & {N_{sb} > 2}\end{matrix} \right.$

A mirroring function ƒ_(m)(i) is given as [Equation 5].

$\begin{matrix}{{f_{m}(i)} = \left\{ \begin{matrix}{i\mspace{14mu}{mod}\mspace{14mu} 2} & {N_{sb} = \begin{matrix}{1\mspace{14mu}{and}\mspace{14mu}{intra}\mspace{14mu}{and}} \\{{inter}\text{-}{subframe}\mspace{14mu}{hopping}}\end{matrix}} \\\begin{matrix}{{CURRENT\_ TX}{\_ NB}} \\{{mod}{\mspace{11mu}\;}2}\end{matrix} & {N_{sb} = \begin{matrix}{1\mspace{14mu}{and}} \\{{inter}\text{-}{subframe}\mspace{14mu}{hopping}}\end{matrix}} \\{c\left( {i \cdot 10} \right)} & {N_{sb} > 1}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$where ƒ_(hop)(−1)=0 and CURRENT_TX_NB represents the transmission numberfor a TB transmitted in slot n_(s). A pseudorandom sequence generationfunction c(i) (refer to 3GPP TS36.211, 7.2) is initialized:c_(init)=N_(ID) ^(cell) for frame structure type 1 andc_(init)=2⁹·(n_(f) mod 4)+N_(ID) ^(cell) from the start of each frame,for frame structure type 2.

In other words, in type 2 hopping, mirroring is applied, that is, thesequence of using transmission resources in a subband is reversed, whilehopping is performed on a subband basis according to the hoppingfunction ƒ_(hop)(i). The hopping function is determined by apseudorandom sequence c(i) which is a function of a cell ID (a mirroringpattern is also a function of a cell ID). Therefore, the same hoppingpattern is used for all UEs within one cell. Cell-specific mirroring maybe used in type 2 hopping.

FIG. 6 illustrates examples of type 2 hopping for the number of subbandsN_(sb) of 4. In an example of FIG. 6(a), a Virtual RB (VRB) 601 hops byone subband in the first slot and by two bands in the second slot. In anexample of FIG. 6(b), mirroring is applied to the second slot.

Synchronization Acquisition of D2D UE

Now, a description will be given of synchronization acquisition betweenUEs in D2D communication based on the foregoing description in thecontext of the legacy LTE/LTE-A system. In an OFDM system, iftime/frequency synchronization is not acquired, the resulting Inter-CellInterference (ICI) may make it impossible to multiplex different UEs inan OFDM signal. If each individual D2D UE acquires synchronization bytransmitting and receiving a synchronization signal directly, this isinefficient. In a distributed node system such as a D2D communicationsystem, therefore, a specific node may transmit a representativesynchronization signal and the other UEs may acquire synchronizationusing the representative synchronization signal. In other words, somenodes (which may be an eNB, a UE, and a Synchronization Reference Node(SRN, also referred to as a synchronization source)) may transmit a D2DSynchronization Signal (D2DSS) and the remaining UEs may transmit andreceive signals in synchronization with the D2DSS.

The D2DSS may have a transmission period equal to or larger than 40 ms.One or more symbols may be used for D2DSS transmission in a subframe.

D2DSSs may include a Primary D2DSS (PD2DSS) or a Primary SidelinkSynchronization Signal (PSSS) and a Secondary D2DSS (SD2DSS) or aSecondary Sidelink Synchronization Signal (SSSS). The PD2DSS may beconfigured to have a similar/modified/repeated structure of a Zadoff-chusequence of a predetermined length or a Primary Synchronization Signal(PSS), and the SD2DSS may be configured to have asimilar/modified/repeated structure of an M-sequence or a SecondarySynchronization Signal (SSS).

A D2D UE should select a D2D synchronization source based on the samepriority criterion. In an out-of-coverage situation, if the signalstrengths of all received D2DSSs are equal to or less than apredetermined value, a UE may be a synchronization source. If UEssynchronize their timing with an eNB, the synchronization source may bethe eNB and the D2DSS may be a PSS/SSS. A D2DSS of a synchronizationsource derived from the eNB may be different from a D2DSS of asynchronization source which is not derived from the eNB.

A Physical D2D Synchronization Channel (PD2DSCH) may be a (broadcast)channel carrying basic (system) information that a UE should firstobtain before D2D signal transmission and reception (e.g., D2DSS-relatedinformation, a Duplex Mode (DM), a TDD UL/DL configuration, a resourcepool-related information, the type of an application related to theD2DSS, etc.). The PD2DSCH may be transmitted in the same subframe as theD2DSS or in a subframe subsequent to the frame carrying the D2DSS.

The D2DSS may be a specific sequence and the PD2DSCH may be a sequencerepresenting specific information or a codeword produced bypredetermined channel coding. The SRN may be an eNB or a specific D2DUE. In the case of partial network coverage or out of network coverage,the SRN may be a UE.

In a situation illustrated in FIG. 7, a D2DSS may be relayed for D2Dcommunication with an out-of-coverage UE. The D2DSS may be relayed overmultiple hops. The following description is given with the appreciationthat relay of an SS covers transmission of a D2DSS in a separate formataccording to a SS reception time as well as direct Amplify-and-Forward(AF)-relay of an SS transmitted by an eNB. As the D2DSS is relayed, anin-coverage UE may communicate directly with an out-of-coverage UE.

Now, a description will be given of a signal transmission method, afrequency resource hopping method, and a subframe indexing method, forD2D communication based on the above description. FIG. 8 illustrates anexemplary resource pool in a D2D communication environment. In FIG.8(a), a first UE (UE 1) may select a resource unit corresponding tospecific resources from a resource pool which is a set of resources andmay transmit a D2D signal in the selected resource unit. A second UE (UE2) may be notified of a configuration of the resource pool in which UE 1may transmit a signal and may detect a signal transmitted by UE 1accordingly. The resource pool configuration may be transmitted insystem information by an eNB. In the absence of information about theresource pool in the system information, the resource pool configurationmay be signaled upon the UE's request. In the case of a UE outside thecoverage of the eNB, another UE (e.g., a D2D relay UE) may indicate theresource pool configuration to the out-of-coverage UE or theout-of-coverage UE may use a predetermined resource area.

A resource pool may include a plurality of resource units and a UE maytransmit a D2D signal in one or more of the resource units. FIG. 8(b)illustrates exemplary resource units. Specifically, a total of NF×NTresource units may be defined by dividing total frequency resources intoNF parts and total time resources into NT parts. Further, the resourceunits may be repeated in every period of NT subframes. Or the index of aPhysical Resource Unit (PRB) to which one logical resource unit ismapped may be changed over time or in a predetermined pattern in orderto achieve time diversity or frequency diversity. In this resource unitstructure, a resource pool may mean a set of resource units availablefor D2D signal transmission of a UE.

A resource pool may be identified by the type of a D2D signaltransmitted in the resource pool. For example, resources pools may bedefined respectively for a D2D control channel (a Scheduling Assignment(SA)), a D2D data channel, and a D2D discovery channel. Further, aplurality of resource pools may be configured for each D2D signal type.The SA may be a signal including information such as the position ofresources used for transmission of a subsequent D2D data channel at eachtransmitting UE, a Modulation and Coding Scheme (MCS) needed fordemodulation of the D2D data channel, a (transmitting or receiving) UEID, a Multiple Input Multiple Output (MIMO) transmission scheme, atiming advance, etc. This signal may be multiplexed with D2D data in thesame resource unit, for transmission. In this case, an SA resource poolmay refer to a pool of resources in which an SA and D2D data aremultiplexed and transmitted. A resource pool for a D2D data channel mayrefer to a pool of resources indicated by an SA, in which a transmittingUE transmits user data. If an SA can be multiplexed with D2D data andtransmitted in the same resource unit, only a D2D data channel withoutSA information may be transmitted in the resource pool for the D2D datachannel. In other words, an RE used for transmitting SA information inan individual resource unit of the SA resource pool is also used fortransmitting D2D data in the D2D data channel resource pool. A resourcepool for a discovery signal refers to a resource pool for a message inwhich a transmitting UE transmits information such as its ID so that aneighbor UE may discover the transmitting UE. Similarly to a PBCH, aPD2DSCH is a channel transmitted together with a D2DSS, includinginformation about a system bandwidth, a TDD configuration, and a systemframe number.

In spite of the same D2D signal type/content, different resource poolsmay be used depending on the transmission and reception properties ofD2D signals. For example, different resource pools may be defined forthe same D2D data channel or discovery message, depending on a D2Dsignal transmission timing determination scheme (e.g., whether a D2Dsignal is transmitted at a reception time of an RS or with apredetermined timing advance applied to the reception time), a resourceallocation scheme (e.g., whether transmission resources of an individualsignal are indicated to an individual transmitting UE by an eNB orselected from a resource pool by the individual transmitting UE), asignal format (e.g., the number of symbols that each D2D signal occupiesin one subframe or the number of subframes used for transmission of oneD2D signal), the strength of a signal received from an eNB, thetransmission power of a D2D UE, etc. For the convenience of description,in D2D communication, a scheme in which an eNB indicates transmissionresources directly to a transmitting D2D UE is referred to as mode 1,whereas a scheme in which an eNB configures a transmission resource areaand a UE directly selects transmission resources from the transmissionresource area is referred to as mode 2. In D2D discovery, a scheme inwhich an eNB indicates resources directly is referred to as type 2,whereas a scheme in which a UE selects transmission resources directlyfrom a predetermined resource area or a resource area indicated by aneNB is referred to as type 1.

Hereinbelow, a frequency hopping scheme for transmission of a D2D signalis proposed. For reference, type 1/2 hopping should be distinguishedfrom type 1/2 discovery in the following description. Type 1/2 hoppingrefers to a frequency hopping scheme in the LTE system, whereas type 1/2discovery is defined according to resource allocation schemes for D2Ddiscovery. Therefore, type 1/2 hopping is applicable in discovery type1/2 and communication mode 1/2. Thus, these terms should not beconfused.

In the legacy PUSCH hopping scheme as described before, a frequencyposition is changed according to CURRENT_TX_NB in type 1 hopping andaccording to a subframe (slot) index in type 2 hopping. When a D2Dsignal is transmitted, an eNB indicates a Time-Resource Pattern forTransmission (T-RPT) and also the position of frequency resources inmode 1.

A D2D UE may map a block of complex-valued symbols to PRBs and then maygenerate and transmit an SC-FDMA signal. For a detailed description ofthe mapping, a UL signal transmission part defined in a 3GPPspecification may be referred to. If frequency hopping is enabled duringthe mapping, the lowest the indexes of the PRBs may be changed between afirst PRB index and a second PRB index (the first and second PRB indexesmay be determined by [Equation 1]) according to a change in thetransmission number for a TB. If the block of complex-valued symbols isa D2D communication signal (i.e., in the case of D2D signaltransmission), the transmission number for a TB may be replaced with theindex of a subframe in a D2D resource pool. That is, hopping isperformed according to a change in a subframe index, not a change in thetransmission number for a TB (CURRENT_TX_NB, which indicates the numberof transmissions that have taken place for the MAC PDU).

In other words, each time a subframe index is changed, resourcescarrying a D2D packet in a resource pool for discovery or D2Dcommunication information are shifted in frequency. This scheme may beimplemented by allocating virtual frequency resources and mapping thevirtual frequency resources to physical resources in a predeterminedrule according to a subframe index. For example, if type 1 PUSCH hoppingis applied to D2D communication, each transmitting D2D UE determines theposition of frequency resources according to a subframe index,irrespective of CURRENT_TX_NB.

The indexes of the subframes of the D2D resource pool may be obtained byreindexing only the subframes of the D2D resource pool. In other words,a hopping pattern is determined according to a relative subframe indexwithin the D2D resource pool by reindexing the subframes of the D2Dresource pool. According to this scheme, when it is hard to know theaccurate indexes of subframes in each resource pool (e.g., in the caseof D2D resource pools of two asynchronous adjacent cells, a UE of aspecific cell may know only relative subframe indexes of the D2Dresource pool of the other cell, having difficulty in acquiring accuratesubframe indexes of the D2D resource pool) or UL subframes are notlocated consecutively in TDD, hopping is performed using the relativepositions of subframes in the D2D resource pool. The scheme forreindexing the UL subframes of a D2D resource pool and performingfrequency shifting each time a reindexed subframe index is changed isdifferent from the afore-proposed scheme for performing frequencyshifting each time a subframe index is changed in that not actualsubframe indexes but new subframe indexes produced by reindexingsubframes of a D2D resource pool are used for hopping. In type 2 PUSCHhopping, for example, n_(s) is not a slot (or subframe) index but a slot(or subframe) index produced by reindexing the subframes of a D2Dresource pool.

In regard to subframe reindexing, the subframes of a resource pool for aD2D communication signal may be reindexed, starting with a first ULsubframe after the end of the resource pool for a D2D control signal(i.e., the SA resource pool). In mode 1, a D2D UE may determine aresource pool for a D2D control signal and then a resource pool for aD2D communication signal based on the resource pool for a D2D controlsignal. The UE may transmit a communication signal using the determinedresource pool for a D2D communication signal. Herein, the subframes ofthe resource pool for a D2D communication signal were reindexed,starting with a first UL subframe after the end of the resource pool fora D2D control signal. That is, relative subframe indexes of D2Dsubframes may be defined using the SA resource pool. For example,subsequent D2D subframes may be reindexed with respect to the firstsubframe of the SA resource pool, or the subframe reindexing may startwith a first UL subframe following the SA resource pool.

In a specific reindexing method, a modulo 10 operation may be performed,while a subframe index is increased, starting from the first subframe ofthe resource pool for a D2D communication signal. Subframes may bereindexed in different manners in FDD and TDD. For example, the firstsubframe following a last subframe of the resource pool for a D2Dcontrol signal may be reindexed as subframe 0 in FDD, whereas the firstUL subframe following the SA pool may be reindexed as subframe 0 in TDDbecause the subframe following a last subframe of the resource pool fora D2D control signal (i.e., the subframe following an SA) may be a DLsubframe or a special subframe. If a D2D resource pool is not defined asdescribed above, subframes may be reindexed based on an SA pool andfrequency hopping may be performed based on the reindexed subframeindexes. If a plurality of resource pools are consecutively configured,subframes may be reindexed sequentially, starting with the first ULsubframe after every SA pool as subframe 0. The subframe indexes startwith 0 and increase sequentially in the subframe reindexing method. Thesubframe following subframe 9 may be reindexed again as 0 by modulo 10(modulo 20 in the case of slot indexing). This is because that subframe(slot) indexes do not exceed 9 (19) during scrambling or generation of aDMRS sequence in the legacy LTE system.

Now, hopping will be described in conjunction with subframe/slotindexing. If frequency hopping is used for transmission of a D2Dcommunication signal, the lowest the PRB indexes of PRBs to which theD2D communication signal is mapped may be changed between a first PRBindex and a second PRB index according to a change in the reindexedsubframe indexes. In type 2 hopping (i.e., hopping based on subbands fortransmission of a D2D communication signal), a slot index used indetermining a PRB index to be used may be produced by performing slotreindexing, starting with a slot of the first subframe following aresource pool for a D2D control signal. Referring to [Equation 4] and[Equation 5], a pseudorandom sequence is used in the hopping functionƒ_(hop)(i) and the mirroring function ƒ_(m)(i). In D2D communication, aninitialization parameter for the pseudorandom sequence may be differentfrom an initialization parameter used in a conventional technology. Forexample, N_(ID) ^(cell) may be signaled to a UE by a physical-layersignal or a higher-layer signal or may be preset to a specific value(e.g., 510) in D2D communication. A pseudorandom sequence generator maybe initialized with C_(init)=N_(ID) ^(cell) for frame structure type 1and c_(init)=2⁹·(n_(f) mod 4)+N_(ID) ^(cell) for frame structure type 2.Herein, a radio frame number n_(f) is used because if an HARQretransmission period is 10 ms in TDD, transmission takes placecontinuously in the same subframe index and thus the same ƒ_(hop)(i) andƒ_(m)(i) may be used. In this case, hopping may not be performedsuccessfully. Therefore, different ƒ_(hop)(i) and ƒ_(m)(i) values may beused for different radio frames by differentiating initialization forthe radio frames despite the same subframe index. If D2D communicationis performed on a TDD carrier, N_(f) may be set in one of the followingthree methods.

First, n_(f) may be preset to a specific value (in TDD or irrespectiveof TDD and FDD) (e.g., n_(f)=0). This method overcomes the problem ofcontinuous transmission in the same subframe when D2D subframe indexesare produced by relatively reindexing only the UL subframes of a D2Dresource pool. Further, this method obviates the need for knowing aframe number of a D2D resource pool (or SA pool) of a neighbor cell).

Second, n_(f) may be a specific value that the network signals by aphysical-layer signal or a higher-layer signal. Or n_(f) may be a valueset for each D2D resource area or each SA resource area. Like the firstmethod, this method may be useful when it doesn't matter whether a framenumber is known or not. This method advantageously enables setting ofdifferent hopping patterns for different pools by setting a differentspecific value for each pool.

Third, n_(f) may be a D2D frame number. Particularly, when cellularsubframe indexes are still used without reindexing D2D subframe indexes,D2D frame numbers may be used restrictively. Or D2D frame numbers may beused all the time irrespective of subframe reindexing. For anin-coverage UE, a D2D frame number may be a cellular frame number. Foran out-of-coverage UE, a D2D frame number may be induced by a GPS orsignaled along with a synchronization signal (on a PD2DSCH) by anin-coverage UE. If the D2D frame numbers of a neighbor cell and aserving cell are different, a frame number offset may be signaled fromthe network by a higher-layer signal or a higher-layer signal or the D2Dframe number of the neighbor cell may be explicitly signaled on aPD2DSCH of the neighbor cell by another UE. For detection of a D2Dsignal of the neighbor cell, the D2D signal may be decoded using theframe number of the serving cell+the offset signaled by the higher-layersignal or using the D2D frame number of the neighbor cell.

Meanwhile, n_(f) may be configured in the same manner in FDD as well asin TDD. This is done in order to simplify implementation by performingsimilar operations in TDD and FDD.

The proposed method may be performed in the same manner in both mode 1and mode 2 or in a different manner in each mode. For example, it may beregulated that frequency diversity is maximized by performing theUE-specific frequency hopping scheme (i.e., by performing frequencyshifting each time CURRENT_TX_NB is changed) in mode 1 and the UE-commonfrequency hopping scheme (i.e., the afore-described method for replacingCURRENT_TX_NB with a subframe index) is performed to prevent collisionbetween UEs in mode 2. Or the opposite case is possible, that is, theUE-common frequency hopping scheme may be used to prevent collision inmode 1, whereas the UE-specific frequency hopping scheme may be used toachieve a uniform frequency diversity gain at each selection ofresources in mode 2 because collision is inevitable in mode 2. Likewise,different subframe indexing schemes may be performed in mode 1 and mode2. For example, UL subframes following an SA resource pool may bereindexed in mode 1 and D2D subframes of a D2D communication resourcepool may be sequentially reindexed in mode 2.

Meanwhile, even though a D2D resource pool is defined, subframe indexesmay be reindexed as relative subframe indexes with respect to an SAresource pool. This is done to apply a common D2D subframe indexingscheme to both mode 1 and mode 2.

The foregoing subframe reindexing method may be applied in the samemanner when subframe indexes are needed, as well as when frequencyhopping is performed. For example, a specific one of the proposedmethods may be used in generating a scrambling sequence, generating aDMRS sequence, and determining a CS/OCC.

For a legacy PUSCH, a scrambling sequence is initialized in eachsubframe. If the proposed subframe reindexing method is performed forD2D communication, this means that a subframe index (slot index) usedfor initialization of a scrambling sequence is a reindexed value.Although a scrambling sequence may not be initialized in each subframe,this case may impose a constraint on implementation because a UE shouldachieve an unbounded sequence unlike the scrambling sequence of thelegacy PUSCH. It may be generalized that in D2D communication, ascrambling sequence may be initialized in every predetermined Nsubframes, not in every subframe and N may be 10, for example. Thisscheme may not significantly increase the implementation complexity of aUE because a scrambling sequence is as long as the scrambling sequenceof the legacy PUSCH but bound.

Likewise, application of the subframe reindexing method to a DMRSsequence and frequency hopping means that legacy PUSCH hopping or a DMRSsequence is initialized at the start of each radio frame and the startof the radio frame is regarded as subframe index 0 produced byreindexing. D2D communication may be characterized in that frequencyhopping (or a DMRS sequence) is initialized in every preset N subrames,not in every 10 subframes. For example, N=4 or N is dependent on a poolsize (the number of D2D subframes in a pool).

Meanwhile, all or a part of the above principle may be applied togeneration of a DMRS and scrambling sequence of a PD2DSCH.

The afore-described scheme in which frequency hopping is performed basedon a subframe index, not according to a change in CURRENT_TX_NB beingthe transmission number for a TB may prevent collision caused by hoppingbetween UEs having different T-RPTs. This will be described withreference to FIG. 9. FIG. 9 illustrates hopping patterns for UE 1 and UE2 having different T-RPTs. FIG. 9(a) illustrates a case in which ahopping pattern is changed according to a change in the transmissionnumber for a TB, CURRENT_TX_NB and FIG. 9(b) illustrates a case in whicha hopping pattern is changed according to a subframe index. In FIG.9(a), although UE 1 and UE 2 transmit initial TBs in differentsubframes, they transmit the second TBs in the same subframe accordingto the T-RPTs. Since hopping is performed according to CURRENT_TX_NB,both UE 1 and UE 2 perform hopping, thus causing resource collision asillustrated in FIG. 9(a). Compared to the case illustrated in FIG. 9(a),hopping is performed according to a change in a subframe index in FIG.9(b). UE 1 and UE 2 transmit initial TBs in different subframes as inFIG. 9(a) and then the second TBs without collision after hopping.

Also, if subframe indexes were reindexed within a D2D resource pool, acommunication signal transmitted by a D2D UE of a neighbor cell may bereceived. More specifically, as a D2D UE receives an SA of the neighborcell, the D2D UE may be aware of the transmission timing of acommunication signal of the neighbor cell. However, the D2D UE does notknow a subframe number of the neighbor cell and thus will receive acommunication signal from the neighbor cell based on a subframe numberof its serving cell. In this case, unless the subframe number of theserving cell is coincidentally identical to the subframe number of theneighbor cell, the D2D UE may not successfully receive a communicationsignal (a scrambling sequence, DMRS, hopping pattern, etc. based on asubframe index) from the neighbor cell. Therefore, the D2D UE may beallowed to receive a D2D communication signal from a neighbor-cell UE byreindexing the indexes of subframes in a D2D subframe pool as in anembodiment of the present invention.

A hopping scheme according to another embodiment of the presentinvention will be described below.

Hopping may be performed based on CURRENT_TX_NB during D2D signaltransmission. That is, each time CURRENT_TX_NB is changed, the positionof a frequency area is changed. This hopping scheme may advantageouslymaximize the frequency diversity of each D2D packet. In type 1 hopping,for example, a D2D signal is transmitted at a frequency position shiftedby a predetermined frequency offset (e.g., a half of the number of RBsin a PUSCH region). The size of the frequency offset may bepredetermined or signaled to a UE by a physical-layer signal or ahigh-layer signal. Particularly, the size of the frequency offset issignaled in RBs or in units of a minimum or maximum resource unit sizeof a D2D signal.

CURRENT_TX_NB may be initialized to 0 each time an initial MAC PDU istransmitted within a D2D resource period and may be increased by 1 eachtime the same MAC PDU is transmitted. In this case, frequency diversitymay be maximized because hopping is applied to each MAC PDU. Suchhopping based on CURRENT_TX_NB is illustrated in FIG. 10(a).

Or to perform hopping in the manner illustrated in FIG. 10(b),CURRENT_TX_NB may be initialized to 0 in each D2D resource period andincreased by 1 each time a transmission takes place within the D2Dresource period. That is, a new parameter (e.g., TX_NB_IN PERIOD) isdefined and this parameter is increased by 1 at each transmission withinthe period. This hopping scheme advantageously simplifies a hoppingpattern because a signal is transmitted in a shifted frequency area ateach transmission and the frequency area is shifted irrespective of thenumber of MAC PDUs.

The afore-described hopping schemes (frequency hopping types) accordingto the embodiments of the present invention may be changed depending ontransmission modes.

In a first method, a hopping pattern configured for use in a PUSCH bythe network may be used in mode 1/2. For example, if the networkconfigures type 2 hopping for a PUSCH, a D2D signal is also transmittedbased on a type 2 hopping pattern. To enable receiving D2D UEs todetermine a used hopping pattern, the network may signal a hopping typeand higher-layer parameters (e.g., N_(RB) ^(HO) and N_(sb)) based on thehopping type to UEs by a physical-layer signal or a higher-layer signal.A cell ID is needed for type 2 PUSCH hopping (to determine a subbandhopping pattern and a mirroring pattern). The cell ID may be fixed to aspecific value or signaled by a physical-layer signal or a higher-layersignal. Or the mirroring pattern and the subband hopping pattern may bepredetermined patterns or patterns linked to a specific ID. For example,a subband size may be 1 and subband hopping is not always performed,while the mirroring pattern may be set to 1010 . . . . For anout-of-coverage UE, these parameters and the hopping type may be presetto specific values. This method may advantageously avoid collisionbetween a Wide Area Network (WAN) signal and a D2D signal because thelegacy cellular signal and the D2D signal have the same hopping pattern.These hopping parameters may be set separately for each D2D resourcepool. For this purpose, the network may signal the hopping parametersfor each D2D resource pool to the UE by a physical-layer signal or ahigher-layer signal. For example, a specific D2D resource pool may usetype 2 PUSCH hopping and another D2D resource pool may use type 1 PUSCHhopping. A hopping mode, parameters, and whether hopping is performed ornot may be determined differently depending on a discovery type and acommunication mode, and a different hopping method may be applied toeach discovery or communication resource pool.

In a second method, hopping configured for use in a PUSCH by the networkmay be used in mode 1, whereas a predefined hopping pattern may be usedfor D2D communication in mode 2. The predefined hopping pattern may befixed to a specific one of legacy hopping patterns used for a PUSCH, ormay be one of the afore-described hopping schemes according to theembodiments of the present invention or a newly defined hopping pattern.It may be regulated that type 1 PUSCH hopping is always used in mode 2.Parameters used for type 1 hopping (a frequency shift size N_PUSCH_RB/2or +/−N_PUSCH_RB/4, N_PUSCH_RB, and a hopping offset) may be parametersfor a D2D resource pool configuration. For example, N_PUSCH_RB may bethe frequency resource size of a D2D resource pool, and the hoppingoffset may be determined by the starting and ending points of the D2Dfrequency resource pool. The network may determine whether frequencyhopping is applied or not. A frequency hopping mode (or a non-frequencyhopping mode) may be set as a default mode for an out-of-coverage UE.

In a third method, aside from a legacy hoping type indicated for a PUSCHby the network, a predetermined hopping pattern may be used in mode1/mode 2. The predetermined hopping pattern may be fixed to a specifictype in the legacy PUSCH hopping scheme, may be set to one of theafore-described hopping schemes according to the embodiments of thepresent invention, or may be a third hopping pattern. Parameters usedfor the hopping (a frequency shift size N_PUSCH_RB/2 or +/−N_PUSCH_RB/4,N_PUSCH_RB, and a hopping offset) may be determined using parameters fora D2D resource pool configuration. For example, N_PUSCH_RB may be thefrequency resource size of a D2D resource pool, and the hopping offsetmay be determined by the starting and ending points of the D2D frequencyresource pool. This method advantageously allows RRC_IDLE-statereceiving D2D UEs to effectively receive a D2D signal because they maydetermine the hopping pattern of the D2D signal without receiving anadditional parameter. Despite the advantage, the third method may causecollision with the hopping pattern of a PUSCH. To avoid the problem, aneNB should perform scheduling in such a manner that collision may notoccur between a WAN PUSCH and a D2D PUSCH. It may be generalized thatwhether frequency hopping is performed is determined for each pool by aphysical-layer signal or a higher-layer signal in mode 2 and a presethopping mode is used for an out-of-coverage UE. For this purpose, thenetwork may signal hopping parameters for each D2D resource poolseparately to UEs by a physical-layer signal or a higher-layer signal.For example, a specific D2D resource pool may use type 2 PUSCH hoppingand another D2D resource pool may use type 1 PUSCH hopping. A hoppingmode, parameters, and whether hopping is performed or not may bedetermined differently depending on a discovery type and a communicationmode, and a different hopping method may be applied to each discovery orcommunication resource pool.

Meanwhile, for an SA or type 1 discovery, a frequency hopping type maybe preset so that receiving D2D UEs may decode a signal without anyadditional signaling. One or more of the afore-described hoppings may beapplied to the SA and/or type 1 discovery. A part of the afore-describedmethods are applicable to discovery.

Configurations of Apparatuses According to Embodiment of the PresentInvention

FIG. 11 is a block diagram of a transmission point and a UE according toan embodiment of the present invention.

Referring to FIG. 11, a transmission point 10 according to the presentinvention may include a Reception (Rx) module 11, a Tx module 12, aprocessor 13, a memory 14, and a plurality of antennas 15. Use of theplurality of antennas 15 means that the transmission point 10 supportsMIMO transmission and reception. The reception module 11 may receive ULsignals, data, and information from a UE. The Tx module 12 may transmitDL signals, data, and information to a UE. The processor 13 may provideoverall control to the transmission point 10.

The processor 13 of the transmission point 10 according to theembodiment of the present invention may perform necessary operations inthe afore-described embodiments.

Besides, the processor 13 of the transmission point 10 processesreceived information and information to be transmitted to the outside ofthe transmission point 10. The memory 14 may store the processedinformation for a predetermined time and may be replaced with acomponent such as a buffer (not shown).

Referring to FIG. 11 again, a UE 20 according to the present inventionmay include an Rx module 21, a Tx module 22, a processor 23, a memory24, and a plurality of antennas 25. Use of the plurality of antennas 25means that the UE 20 supports MIMO transmission and reception using theplurality of antennas 25. The Rx module 21 may receive DL signals, data,and information from an eNB. The Tx module 22 may transmit UL signals,data, and information to an eNB. The processor 23 may provide overallcontrol to the UE 20.

The processor 23 of the UE 20 according to the embodiment of the presentinvention may perform necessary operations in the afore-describedembodiments.

Besides, the processor 23 of the UE 20 processes received informationand information to be transmitted to the outside of the UE 20. Thememory 24 may store the processed information for a predetermined timeand may be replaced with a component such as a buffer (not shown).

The above transmission point and UE may be configured in such a mannerthat the above-described various embodiments of the present inventionmay be implemented independently or in combination of two or more. Aredundant description is omitted for clarity.

The description of the transmission point 10 in FIG. 11 is applicable toa relay as a DL transmitter or a UL receiver, and the description of theUE 20 in FIG. 11 is applicable to a relay as a DL receiver or a ULtransmitter.

The embodiments of the present invention may be implemented by variousmeans, for example, in hardware, firmware, software, or a combinationthereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

The detailed description of the preferred embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the preferred embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. Accordingly, the inventionshould not be limited to the specific embodiments described herein, butshould be accorded the broadest scope consistent with the principles andnovel features disclosed herein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentinvention or included as a new claim by a subsequent amendment after theapplication is filed.

INDUSTRIAL APPLICABILITY

The afore-described embodiments of the present invention are applicableto various mobile communication systems.

What is claimed is:
 1. A method for transmitting a sidelinkcommunication signal by a sidelink User Equipment (UE) in a wirelesscommunication system, the method comprising: determining a resource poolof a sidelink control signal; determining a resource pool for a sidelinkcommunication signal based on the resource pool of the sidelink controlsignal; and transmitting the sidelink communication signal based on theresource pool for the sidelink communication signal, wherein subframesof the resource pool for the sidelink communication signal are firstlyreindexed, starting from a first subframe following a last subframe ofthe resource pool of the sidelink control signal, wherein the firstlyreindexed subframes are secondly reindexed with a modulo 10 operation.2. The method according to claim 1, wherein the secondly reindexedsubframes are used for frequency hopping of the sidelink communicationsignal.
 3. The method according to claim 1, wherein slot indexes of thesecondly reindexed subframes are used for frequency hopping of thesidelink communication signal.
 4. The method according to claim 1,wherein if a duplex mode of the sidelink UE is Time Division Duplex(TDD), the first subframe is an uplink subframe following the lastsubframe of the resource pool of the sidelink control signal.
 5. Asidelink User Equipment (UE) for transmitting a sidelink communicationsignal in a wireless communication system, the UE comprising: atransmission module; and a processor, wherein the processor isconfigured to determine a resource pool of a sidelink control signal,determine a resource pool for a sidelink communication signal based onthe resource pool of the sidelink control signal, and transmit thesidelink communication signal using the resource pool for the sidelinkcommunication signal, and wherein subframes of the resource pool for thesidelink communication signal are firstly reindexed, starting from afirst subframe following a last subframe of the resource pool of thesidelink control signal, wherein the firstly reindexed subframes aresecondly reindexed with a modulo 10 operation.
 6. The UE according toclaim 5, wherein the secondly reindexed subframes are used for frequencyhopping of the sidelink communication signal.
 7. The UE according toclaim 5, wherein slot indexes of the secondly reindexed subframes areused for frequency hopping of the sidelink communication signal.
 8. TheUE according to claim 5, wherein if a duplex mode of the sidelink UE isTime Division Duplex (TDD), the first subframe is an uplink subframefollowing the last subframe of the resource pool of the sidelink controlsignal.